The invention relates to a fuel injection system comprising a pump which generates injection pressure and at least one fuel injection nozzle having a valve needle associated therewith with the valve needle being arranged to be loaded in the closing direction by means of a closing spring positioned in a chamber and additionally by fuel which leaks along the valve needle into the spring chamber and is dammed up when it flows through an outlet provided in proximity to said chamber. In a known fuel injection system of this design, the pressure in the spring chamber changes in proportion to the quantity of fuel that leaks into it and in proportion to the position of the valve needle. The fuel quantity, for its part, is directly dependent on the period of time during which pressure prevails in the pressure chamber of the fuel injection nozzle. An opening characteristic of the valve needle is striven for by means of a supplementary piston which is hydraulically controlled and acts on the valve needle, where with this opening characteristic the valve needle has a significantly smaller closing force load during starting than at higher rmp. Because of this, the injection times during idling are particularly short and increase as the engine rpm increases. However, short injection durations during idling are not desirable.